This invention relates generally to lapping or grinding of bodies having transducers, more particularly, it relates to the monitoring of the lapping of transducers at the lapping surface.
Many present day fabrication techniques include a grinding or lapping step in which a workpiece or body is lapped by a lapping mechanism such as a lap plate. Lapping frequently serves purposes other than just polishing of the surface being lapped. In many situations, the purpose of lapping is also to trim in a controlled manner one or more elements of the body being lapped at the surface being lapped, i.e., the lapping surface. For example, the body may have a number of embedded parts which are to be lapped to an accurate height or width.
Currently, lapping plays a key part in the fabrication of transducers such as magnetic recording heads embedded in a body of silicon. The body is later used as an air bearing slider, while the lapping surface becomes the air bearing surface of the slider. The height of the heads is trimmed during the lapping operation at the lapping surface. This lapping surface is orthogonal to the surface of the silicon wafer on which the heads are fabricated. The lapping operation removes material from the head, and in particular the stripe of the head such that the height of the stripe is reduced to achieve the sensitivity required. Typically, the final height of such stripe is less than 1 micron. The variation in stripe height must also be quite small to meet the signal requirements for modern disk drives. This variation is currently about 50 nm.
One common device used to control the lapping process is an xe2x80x9celectronic lapping guidexe2x80x9d ELG. The ELG is a resistor which is fabricated together with the read head element and is in a well-defined orientation with respect to the head element. Any narrowing of the ELG reflects an equivalent narrowing of the stripe belonging to the head. Further information about ELGs can be found in U.S. Pat. No. 4,675,986 to Yen.
The prior art describes the use of the head itself and its changing electrical property, e.g., its resistance, for controlling the lapping process. One of the problems with using the head itself as a lapping indicator is that the lead resistance necessary to connect to it during lapping decreases the accuracy with which the actual head resistance can be measured. Hence, one commonly accepted practice is to use an ELG having a larger resistance than the head, thereby improving the resolution of the measurement.
Another difficulty encountered in using the head as the lapping indicator is that the head is very narrow. This narrow width, coupled with lead connections with a height much larger than the width of the head, results in a nonlinear relationship between stripe height and resistance.
The prior art teaches two generic approaches to the lapping of heads including magnetoresistive (MR) and giant magnetoresistive (GMR) heads. The first is to fabricate a single row of heads on a silicon wafer and lap that row of heads simultaneously. More information about this process can be found in U.S. Pat. No. 5,559,051 to Voldman et al.
Most or all of the heads have an associated ELG for monitoring their height during the lapping process. The connections to the ELGs are typically established by pressure contacts or wirebonded contacts. It is rather difficult to make pressure contacts reliably. Therefore, large contact forces have to be used. Even so, some lapping process tolerance is needed to accommodate incomplete contacts to ELGs monitoring some of the heads. The contact assemblies used to establish contact with the ELGs have precise dimensions, necessitated by the small head and contact size, and may be rather expensive. Wirebonding can also be an expensive alternative.
The second generic lapping approach handles groups of rows together. A single row is lapped, then cut from the group, typically with a diamond saw. In this case it is convenient to place the ELG contacts in the kerf, (or the area of the saw cut), above the row being lapped. When the lapped row is cut off, the saw removes the ELG contacts. Contact is commonly made using pressure contacts between a flex circuit and the ELG contact on the group of rows (also referred to as quad). The flex circuit carries the signals to the resistance measuring device located elsewhere.
A substantial problem arises because of the contact force needed to make contact with the ELGs. The problem is due to the elastic distortion generated upon loading, and the subsequent relaxation upon unloading. Specifically, the body is lapped to a high degree of flatness in the loaded state and, upon unloading, becomes distorted in the opposite direction to that which was imposed during the loading process.
Another problem is becoming more crucial as lapping precision is being improved. There is an uncertainty in the resistance measurement of the ELGs due to the resistance of the leads between the ELG and the measurement point. More precise 4-point resistance test could overcome this problem, but would require more contacts to the ELG and would further contribute to the elastic distortion problem.
Therefore, it would be an advance to provide a method for monitoring the lapping of transducers such as magnetoresistive heads while avoiding the problems associated with elastic deformation and allowing for very precise lapping control and accurate resistance readings.
Accordingly, it is a primary object of the present invention to provide a lapping monitor and lapping method which reduce the loading or contact forces placed on the body bearing the transducers. Specifically, it is an object of the invention to reduce the loading while at the same time making it possible to perform 4-point resistance tests to accurately monitor the lapping of the transducers.
It is another object of the invention to adapt the lapping monitor to the lapping of magnetoresistive heads in air bearing sliders.
These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.
These objects and advantages are attained by a lapping monitor for monitoring the lapping of a lapping surface of a body such as a silicon body, a wafer or wafer portion. The body has at least one transducer which has a height that has to be lapped, e.g., in order to achieve a well-defined desired transducer height. The lapping monitor has a lap unit for lapping the lapping surface. At least one lapping indicator is mounted close to the transducer such that it indicates the height of the transducer. A control block is provided in the body at a certain distance from the lapping indicator or indicators. The control block is set to receive indication of the height of the transducer from the lapping indicators. An electrical connection for communication between the lapping indicators and the control block is also provided. Test contacts are provided on the control block for establishing an external connection to the control block, e.g., for passing on the information about transducer heights to external circuitry for further processing.
In one embodiment, the lapping monitor also includes a contact assembly for contacting the test contacts to establish the external connection. The contact assembly is equipped with contacting elements such as pins or other elements which can make reliable electrical contact with the test contacts. The test contacts are preferably located on the control block itself. The electrical contact can be established by pressing the contact assembly, and specifically its contacting elements against the test contacts. Alternatively, the electrical contact can be established by wirebonds to the test contacts.
The lapping monitor is convenient for use in situations where there are numerous transducers and lapping indicators. In such situations each lapping indicator can be associated with one of the transducers whose height is being lapped. Alternatively, one lapping indicator can be used to indicate the lapping height of more than one of the transducers. When monitoring the lapping of a number of transducers with a number of lapping indicators the control block is preferably equipped with a multiplexing logic for multiplexed communication with the lapping indicators. In this manner a large number of lapping indicators can be efficiently interrogated about the lapping height of the transducers.
The lapping monitor of the invention is particularly well-suited for performing 4-point resistance tests on the lapping indicators to derive the height of the transducers. To perform this test, control block has a corresponding testing logic.
The lapping monitor of the invention can be used in situations where the body is a silicon wafer or a part thereof, e.g., a segment cut from a silicon wafer with a set of transducers. The set of transducers can be a set of magnetoresistive transducer heads for reading and writing data in magnetic media. Exemplary magnetoresistive transducer heads include MR heads, GMR heads or other advanced heads. The transducer heads can be mounted in a row on the silicon wafer and the control block can be located at the end of that row.
In another embodiment, the lapping monitor uses a property of the transducer or transducers for monitoring the height to which the one or more transducers have been lapped. In this case the transducer plays the role of the lapping indicator by providing the control block with an indication of the height. The communication takes place over an electrical connection between the transducer or the set of transducers and the control block. In this embodiment a contact assembly for contacting the test contacts on the test block to establish external connection can also be provided. Likewise, the control block can have suitable multiplexing logic for multiplexed communication with the set of transducers. Furthermore, it is also preferable to use the 4-point resistance test when using the transducers themselves to indicate their heights.
In accordance with one method of the invention the monitoring of the lapping of a lapping surface of the body equipped with the one or more transducers is performed by using lapping indicators. In another embodiment of the method, the transducers themselves are used to indicate their height and thus monitor the lapping process. In either embodiment of the method, it is preferable to employ the 4-point resistance test.
The details of the invention are explained in the below detailed description with reference to the attached drawing figures.